In the present invention, novel chromogenic chemical substances are disclosed as molecular tags for organic solvent solutions, especially petroleum products. A method of synthesizing, detecting and quantifying these new substances is also disclosed. The detection methods provides a novel and improved technique for detecting and quantifying some known marker substances. With the present invention, color or fluorescence is developed in a single phase system containing the petroleum product, without need of a separate extraction step.
Proton accepting chemical substances, that at a solution concentration of below about 20 milligrams per litre, impart little or no significant color to organic solvents, have been proposed as markers, or taggants, especially for petroleum-derived fuels, on many occasions. The marker is dissolved in a liquid to be identified, then subsequently detected by performing a simple physical or chemical test on the marked liquid. Markers are sometimes employed by government agencies to ensure that the appropriate tax has been paid on particular grades of fuel. Oil companies also mark their products to help assist in identifying those who have diluted or altered their products. These companies often go to great expense to make sure their branded petroleum products meet certain specifications, for example, volatility and octane number, as well as to provide their petroleum products with effective additive packages containing detergents and other components. Consumers rely upon the product names and quality designations to assure that the product being purchased is the quality desired.
Traditionally, the presence of these substances is detected and optionally quantified by extracting the fuel with an immiscible aqueous or significantly aqueous solution of an acid substance, the precise nature of which can be varied according to the characteristics of the marker substance. The acid reacts with the basic compound to produce a readily visible, more or less intensely colored cation, that is dissolved in the aqueous acid phase. This technique is illustrated in the disclosure of U.S. Pat. No. 5,145,573.
The quantity of marker substance in the extract may also be measured, for instance, by visible light absorption spectrophotometry, the results of which are then compared with a reference standard to determine the original concentration of basic marker in the fuel. It is sometimes necessary to make repeated, typically two or three, extractions of the fuel to recover all the marker originally present in order for complete quantification. Consequently, it is also relatively simple to remove the marker from the marked fuel by this reaction. This is a shortcoming of these prior art basic marker substances; they are relatively easy to remove from fuels by unscrupulous parties who may wish to defraud tax authorities, or individual consumers. For instance, marked low octane gasoline may be laundered to remove the marker enabling fuel to be resold as unmarked, higher price premium fuel. Alternatively, marked #2 fuel oil, sold tax free as home heating oil or railroad or agricultural diesel fuel, may have the marker removed from it in order to resell it at the much higher price of taxed, on road, diesel engine fuel. The lawful tax collection agencies are thereby deprived of their revenues. In the United States, such revenues have increased by about 2 billion dollars since implementing a marker program in 1993.
Additionally, the extracted, separated phase is classifiable as a hazardous waste and presents problems of safe and lawful disposal, especially when examinations are made xe2x80x9cin the field.xe2x80x9d Furthermore, the fuel with which it was in contact may be water wet, making return to its original source undesirable and thus presenting an additional waste disposal problem. By using a developing agent of the present invention, especially hydrocarbon or alcoholic solutions of an organic phosphoric or sulfonic acid, the indicative color or fluorescence of the marker can be made plainly and instantly visible and can be quantified without extraction from the petroleum product.
The rapidity and certainty of the test procedure is very important in field testing to minimize delaying trucks and wrongful impoundment of vehicles. Isotopic labeling can also be useful as a secondary analytical procedure to confirm, independently, results already obtained by chromogenic analysis.
The present invention provides compositions comprising a petroleum product, which forms an organic phase, a marker substance dissolved in the petroleum product, and a non-aqueous acid combined with the marker substance in the organic phase to develop a detectable color. It also includes compositions comprising a petroleum product, which forms an organic phase, a marker substance dissolved in the petroleum product, and an acid combined with the marker substance and petroleum product to develop a detectable color or fluorescence in the organic phase.
Markers for petroleum products are also provided. They have the following structure: 
where A, B, and C, independently of each other, are aromatic carbocyclic moeities, N is nitrogen and R is an alkyl group or hydrogen atom. Further, the present invention provides methods of identifying a petroleum product containing an acid reactable marker by first obtaining a sample of petroleum product containing an acid reactable marker, and then adding to that sample a developing agent comprising a non-aqueous acid or solution to form a single phase in which the acid and marker combine to develop a detectable color.
The present invention provides novel molecular taggants or markers and developing agents for use with them. The developing agents may also be used with preexisting markers that react with an acid. The markers are essentially invisible in liquid petroleum products at an effective level of use but provide a distinctive color and/or fluorescence when contacted by an appropriate developing agent of the present invention. The procedure of the present invention for developing color or fluorescence is simple to perform in the field and the reagents used to develop the color are easy to handle and recycle.
With the present invention, the procedure for detecting and quantifying acid reactive markers, for petroleum-derived compositions, can take place directly in the petroleum product without extraction of an aqueous phase. This reaction is accomplished preferably with a non-aqueous organic acid solution that is miscible with that petroleum product. This combination produces an instant visual or, if desired, instrumental indication of the presence of the marker substance. The marker concentration may be determined accurately by, for instance, standard spectrophotometric procedures. The procedure of the present invention is faster and more convenient than use of aqueous acid extractions to produce a quantitative result and an extended time period to yield complete phase separations. The new procedure also reduces potential environmental disposal problems since the developed, marked product may be returned to its origin; optionally, with neutralization of the acid developer, with, for instance, an aliphatic amine that is miscible with the said petroleum product. It also permits the use of acid reactable marker substances that do not readily extract from the petroleum product under aqueous acid conditions.
Developing reagents of the present invention are symbolized generally by Rxe2x80x94OH where the OH group is part of an acid moeity with a pKa value of 3.5 or less and R is a mono alkyl or aryl sulfonic acid moeity or a mono alkyl or dialkyl phosphoric acid.
The preferred acids for marker development are those which are fully miscible with the petroleum product. In addition, for quantitative analysis the salt they develop, by reaction with the marker substance, should also be completely soluble in the fuel.
The final choice of acid can vary from one system to another according to solubility parameters. For instance, high octane gasolines frequently contain a substantial amount of aromatic hydrocarbons that have good solvency power for the marker substance and developer. Conversely, kerosene fuel and lubricating oils are substantially aliphatic and/or alicyclic in nature and have comparatively poor solvency properties for many marker substances and their salts derived from reaction with acids.
Although organic sulfonic acids like methane sulfonic acid can be used, acids with a more complex organic function are desirable for miscibility purposes. Especially preferred are higher alkylated benzene sulfonic acids, in particular the C10-C20 alkyl substituted benzene sulfonic acids of which dodecylbenzene sulfonic acid is the most convenient of all. This compound is manufactured extensively as the basis of many laundry and other detergents. The dodecyl chain may be either linear or branched, linear compounds are preferred since they biodegrade more readily, both are completely effective in our invention.
As an alternative to the sulfonic acids, mono or di alkyl or aryl esters of phosphoric acid may be used as developer or detector reagents. Many such compounds are available industrially and, as with the organic sulfonic acids, the final choice depends upon the compatibility of the particular fuel with the system being tested. One compound that has a wide spectrum of compatibility, and is especially preferred, is the di (2 ethylhexyl) ester of phosphoric acid.
The quantity of developer to be used in the detection procedure is at least one molar equivalent per mole of marker substance and preferably 2-5 times excess. The acid developer is preferably added in the form of a dilute solution in a hydrocarbon, alcohol or glycol ether. The reason for this is that the marker substance will be at a concentration of 100 mg/L or less in the petroleum product and the molar amount of the developer acid to be used will be very small and inconvenient to add as an undiluted substance. For a gasoline fuel, a fairly volatile solvent, such as toluene, xylene, ethanol or n-propanol is recommended. For less volatile fuels like kerosene, 2 ethyl hexanol or I dodecane may be preferred due to their greater compatibility with this type of system. These solvents are also suitable for use with lube oils and greases. In the latter case, the concentration of dodecylbenzene sulfonic acid may have to be radically increased due to the presence of other bases, especially inorganic compounds like lithium hydroxide, in greases. Generally speaking, the ratio of acid to marker substance may be varied over a broad range of concentrations to optimize marker development in different systems. The concentration of acid used in the present method is typically much less than the aqueous or aqueous alcoholic developer/extractants specified in the prior art.
The activity level of the acid in our invention can be 0.05 molar or even less. This contrasts with a recommended concentration of 2.5-3.0 molar acid used in extraction procedures. Consequently, our developing reagent is less corrosive and potentially much less hazardous to handle than prior art recommendations, especially in field test situations.
Suitable solvents for the acid developer include aliphatic and aromatic hydrocarbons, alcohols, glycols and glycol ethers. The lower alcohols, such as methanol, ethanol and propanol are convenient for this purpose, particularly when the petroleum product is gasoline but most preferred are hydrocarbons like toluene or xylene. For use with other petroleum products, for instance use in conjunction with marked diesel fuels, a less volatile solvent is preferred. Generally, the higher aliphatic and aromatic hydrocarbons are particularly valuable in this respect and especially isooctane, dodecane and other aliphatic hydrocarbons which present a desirable combination of properties including good solvency power and miscibility with petroleum fuels, low vapor pressure at ambient temperatures, high flash points and non mutagenicity. This combination minimizes human health and fire hazards.
The concentration of the acids in solutions of the present invention may be varied over a wide range. It is preferred that enough acid is present to react with all the marker in the fuel sample. For practical reasons a solution of about 0-5-10%, preferably about1%, of acid in solvent is considered desirable for commercial purposes. A solvent will therefore ordinarily make up about 90-99% of the non-aqueous developer solution.
Developing reagents of the present invention may be used, for instance, with either the novel marker substances of this invention or prior art markers such as Solvent Yellow 56 or Solvent Yellow 124.
The preferred novel taggants or marker substances of the invention are aromatic carbocyclic monoazo compounds symbolized by the following generic structure: 
Where A, B and C are aromatic carbocyclic moeities, preferably benzene or naphthalene, N represents nitrogen atoms and R is an alkyl group or hydrogen atom. R is preferably branched or unbranched C1-C20.
Hydrogen atoms attached to units A, B and C may be substituted, optionally, by one or more other atoms or groupings that do no impart appreciable water solubility to the molecule. Typical substituents may be halogen atoms, nitro, alkyl, alkoxy or hydroxy groups, carboxylic esters, carboxamide or sulfonamide functions. Especially useful are substituents like alkyl groups, that enhance solubility of the basic marker substance in organic solvents, particularly the aliphatic hydrocarbons that predominate in many petroleum fuels. Also, where the marker substance is intended to be combusted as part of a fuel, it is very desirable to confine its composition to carbon, hydrogen, nitrogen and oxygen atoms in order to avoid the emission of possible atmospheric pollutants such as sulfur oxides and hydrogen halides.
The monoazo marker compounds of the invention can be prepared by conventional techniques involving either the diazotization of a preferred carbocyclic primary aromatic amine followed by azo coupling to an N arylamino benzeneamine or N aryl naphthaleneamine which is free to undergo azo coupling in the 4 position of the aromatic nucleus with respect to the N aryl amino substituent at position 1.
For practical and economic reasons the preferred primary amines are aniline and its ring alkylated derivatives, especially dodecylaniline. Also valuable are the esters of aminobenzoic acids, the primary function of the ester grouping being to enhance the solubility of the marker substance in hydrocarbon solvents, particularly the aliphatic, naphthenic and alicyclic hydrocarbons that are the major components of gasoline, diesel, home heating and lubricating oils and kerosene.
Alternatively, the preferred compounds of the invention may be synthesized by the diazotization of a 4 amino diphenylamine followed by its azo coupling to a phenol or substituted phenol. Of especial value as coupling components are alkyl phenols whereby the appropriate choice of an alkyl group ensures that the resulting compound has good solubility in the aforementioned aliphatic naphtheneic and alicyclic hydrocarbon solvents.